1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to digital rights management, and more particularly, to consuming a rights object (RO) having an inheritance structure in an environment where the RO is distributed over a plurality of devices.
2. Description of the Related Art
Recently, digital rights management (hereafter, referred to as DRM) has been actively researched and developed. Commercial services using DRM have already been used or will be used. DRM needs to be used because of the following various characteristics of digital content; digital content can be copied and easily distributed.
There were several efforts to protect digital content. Conventionally, digital content protection has been concentrated on preventing non-permitted access to digital content, permitting only people who paid charges to access the digital content. Thus, people who paid charges to the digital content are allowed to unencrypted digital content while people who did not pay charges are not allowed to. In this case, when a person paid charges intentionally distributes the digital content to other people, however, the people can use the digital content without paying charges.
To solve this program, DRM was introduced. In DRM, any one is allowed to freely access encoded digital content, but a license referred to as an RO is needed to decode and execute the digital content.
Referring to FIG. 1, a device 10 obtains digital content from a content provider 20. Digital content provided by the content provider 20 is encrypted, and thus, in order to use the digital content, an RO corresponding to the digital content is needed.
The device 10 can obtain the RO with a license to play the encrypted content from received from an RO issuer 30. To this end, a user should pay charges. The encrypted digital content is decrypted using a key contained in the RO.
The RO issuer 30 makes the content provider 20 prepare an RO issuing detail report. The RO issuer 30 and the content provider 20 may be the same authority.
After obtaining the RO, the device 10 consumes the RO to use the encrypted digital content.
The encrypted digital content can be freely copied and distributed to another device (not shown). However, since an RO contains constraint information such as Count, Interval or Copy, unlike the encrypted digital content, the RO has a limitation in its reuse or replication. Accordingly, the digital content can be more effectively protected by using DRM.
Recent DRM techniques enable content object playback services to be provided to users on a subscription basis by playing back content objects using a plurality of ROs having an inheritance structure. A device generally needs two or more ROs that are in inheritance relationship to use an encrypted content object. A plurality of ROs needed for using a single encrypted content object may be stored in different devices. Therefore, it is necessary to develop methods to efficiently consume a plurality of ROs needed for using a single encrypted content object.
Recently, methods for facilitating the storage and distribution of ROs by managing the ROs with the aid of a portable storage device such as a memory stick or a multimedia card have been developed. However, portable storage devices generally provide poorer operation capabilities than digital content playback devices. Therefore, it is necessary to develop methods to reduce the operation load of a portable storage device when a device consumes a plurality of ROs that are stored in the portable storage device and have an inheritance structure.